Coping with peer adversity is a common occurrence in childhood that markedly increases the risk for psychopathology and adjustment problems. However, little is known about the nature, precursors, correlates, and developmental sequelae of individual differences in children's behavioral patterns of responding to peer difficulties. In addressing this knowledge gap, this proposal is designed to apply the ethological reformulation of Emotional Security Theory (EST-R; Davies & Sturge-Apple, 2007) to advance the study of children's social behavior within agonic peer relationships in relation to the goal of maintaining sense of security in peer contexts. As a first test of the utility of the EST-R for the study of per dynamics, this application seeks to address the following specific aims: (1) identify the nature and developmental course (i.e., stability, change) of individual differences in children's adoption of five security profiles of defending against peer threat, (2) explicate interrelationships betwee the security profiles and the proximal characteristics of the peer ecology, and (4) examine hypothesized specificity in the mental health and social adjustment sequelae of the security profiles over the course of one year. To address these objectives, this application proposes to utilize a rich existing data set that followed a high risk sample of over 238 6- to 11-year-old children through two summer camps spaced one year apart. As a supplement to the project, a novel measurement approach will be implemented to rigorously examine children's patterns of behavioral responding to threatening peer events in naturalistic peer settings using an innovative ethologically-based coding scheme. Within the context of careful observations and a broader multi-method, multi-informant design, the sophisticated multi-level structural equation modeling and pattern-based analyses are designed to offer rigorous tests of the novel, theoretically guided hypotheses. Consequently, the study has the potential to significantly advance knowledge on the developmental nature, precursors, and sequelae of discordant peer relationships with direct implications for improving targeted identification of children at risk an guiding studies that identify distinct causal processes and target mechanisms for change in intervention initiatives. .